[petsc-users] PETSC FVM view gradient

[Thibault Bridel-Bertomeu]

Dear all,

This request stems from the "How to add a source term for PETSCFV ?" thread.
Basically, I would like to output in a VTK file all the components of the
gradient computed using the following piece of code (given sol is a global
representation of the solution over the whole mesh described by the manager
dm with a unique field fvm).

  ierr = PetscFVSetComputeGradients(fvm,PETSC_TRUE);CHKERRQ(ierr);
ierr = DMConvert(dm, DMPLEX, &plex);CHKERRQ(ierr);  ierr =
DMPlexGetDataFVM(plex, fvm, &cellGeom, &faceGeom,
&gradDM);CHKERRQ(ierr);  ierr =
DMCreateLocalVector(plex,&locX);CHKERRQ(ierr);  ierr =
DMPlexInsertBoundaryValues(plex, PETSC_TRUE, locX, 0.0, faceGeom,
cellGeom, NULL);CHKERRQ(ierr);  ierr = DMGlobalToLocalBegin(plex, sol,
INSERT_VALUES, locX);CHKERRQ(ierr);  ierr = DMGlobalToLocalEnd  (plex,
sol, INSERT_VALUES, locX);CHKERRQ(ierr);  ierr =
DMCreateGlobalVector(gradDM, &grad);CHKERRQ(ierr);  ierr =
DMPlexReconstructGradientsFVM(plex, locX, grad);CHKERRQ(ierr);  ierr =
DMCreateLocalVector(gradDM, &locGrad);CHKERRQ(ierr);  ierr =
DMGlobalToLocalBegin(gradDM, grad, INSERT_VALUES,
locGrad);CHKERRQ(ierr);  ierr = DMGlobalToLocalEnd(gradDM, grad,
INSERT_VALUES, locGrad);CHKERRQ(ierr);  ierr =
VecDestroy(&grad);CHKERRQ(ierr);

  ierr = PetscViewerCreate(PetscObjectComm((PetscObject)gradDM),
&viewer);CHKERRQ(ierr);

  ierr = PetscSNPrintf(filename,sizeof
filename,"%s-%03D-gradient.vtu",user->outputBasename,stepnum);CHKERRQ(ierr);

  ierr = PetscViewerSetType(viewer, PETSCVIEWERVTK);CHKERRQ(ierr);
ierr = PetscViewerFileSetName(viewer, filename);CHKERRQ(ierr);

  ierr = VecView(locGrad,viewer);CHKERRQ(ierr);


I am having troubles with a few things I think but I cannot figure out how
to put it together in the right order ...
(i) I am not sure whether VecView should be called with a local or a global
vector
(ii) I can see from the error log that gradDM does not have fields and thus
when it goes through dmplexvtu.c it crashes and cannot write the file. I
tried to add the fvm as a field, but it does not work either, it crashes on
a memory corruption.

Could somebody please advise ?

Thank you very much in advance,

Thibault Bridel-Bertomeu
—
Eng, MSc, PhD
Research Engineer
CEA/CESTA
33114 LE BARP
Tel.: (+33)557046924
Mob.: (+33)611025322
Mail: thibault.bridelbertomeu at gmail.com


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